1. Field of the Invention
The present invention relates to a silicon-carbon composite for a negative active material of a lithium secondary battery, and more particularly to a silicon-carbon composite for a negative active material of a lithium secondary battery, which may reduce volume expansion upon lithium ion insertion and may exhibit superior ionic conductivity and electrical conductivity to thereby maintain high capacity.
2. Description of the Related Art
Secondary batteries are being used as large power storage batteries for electric vehicles or battery power storage systems and small high-performance energy sources for portable electronic devices such as mobile phones, camcorders, notebooks, etc. In order to reduce the size of portable electronic devices and achieve long-term continuous use, secondary batteries able not only to achieve lightness of parts and low power consumption but also which can ensure high capacity despite being small are required.
Recently, in the market for secondary batteries, the development of a negative active material which enables large size, high capacity and high performance has become essential, in order to be used in portable electronic devices and information communication devices, and also in energy storage devices for hybrid vehicles (HEV or PHEV) or power generation systems.
However, highly crystalline carbon-based active materials that are commercially available as a negative active material for a conventional secondary battery have a limited theoretical capacity of 372 mAh/g despite having superior characteristics as active materials for batteries. Hence, the development of a non-carbon-based negative active material is essential to the manufacture of high-capacity and high-performance lithium secondary batteries.
In the non-carbon-based negative active material, silicon (Si) has a high discharge capacity of 4,200 mAh/g and a very low lithium reaction potential of 0.4 V (Li/Li+), and is thus known to be the most appropriate for a negative material.
However, silicon is problematic because volume expansion takes place at up to 400% at a maximum upon insertion (charge) of lithium ions, and thus the capacity is not maintained, and also because of low electrical conductivity or the like, and thereby it is necessary to solve the above problems before silicon can be commercialized as a negative active material.